The present invention relates generally to electrical lighting sources and, more particularly, to electrical lighting sources in illuminated exit signs.
Under current local fire and building codes, buildings to which the public has access are required to have signage therein identifying the exits. Most of these signs are required to exhibit a specific amount of illumination and, oftentimes, must have an emergency backup power source to provide emergency illumination to the light for a specified period of time during periods when utility power to the building is discontinued, thereby facilitating egress of persons from the building.
Traditionally, two 15-watt incandescent lamps driven by 120 volt alternating current (120 VAC) have been employed to provide normal illumination while two 3.6-watt incandescent lamps driven by a self contained emergency battery power supply are used for illumination during power failure situations. A switching or transfer device will automatically operate the emergency backup illumination system when a power failure is detected.
While these traditional exit sign lighting arrangements perform adequately, they do have a few drawbacks. A major drawback is that the incandescent bulbs use large amounts of electric power thus requiring a relatively large emergency battery power supply for use during emergency lighting situations. Furthermore, while the incandescent bulbs provide adequate illumination, such bulbs do not have a long life in service and require frequent replacement.
To alleviate the drawbacks associated with incandescent bulbs, many manufacturers are beginning to utilize light emitting diodes (LEDs) rather than incandescent bulbs in exit signs. Each light emitting diode provides a relatively small amount of light as compared to the traditional incandescent bulbs whereby a large number of light emitting diodes must be used to provide the same amount of illumination offered by the traditional incandescent bulbs.
It is an object of the present invention to provide a novel lighting device for an exit sign using a plurality of light emitting diodes.
It is also an object to provide such a lighting device which allows the light emitting diodes to be powered by both the normal utility electrical power (120 VAC) and, during emergency power situations, an emergency battery power supply and associated charging and transfer circuitry.
Still another object is to provide such a lighting device in which the light emitting diodes are arranged in the exit sign to provide the amount of illumination required by building codes.
A further object is to provide such a lighting device which may be readily and economically fabricated and will enjoy a long life in operation.